The term S-folds denotes F-theory compactifications which involve non-trivial S-duality transformations. In this talk I will discuss 4d N=2 preserving S-folds and the worldvolume theories on D3-branes probing them. They consist of two new infinite series of superconformal theories whose distinction lies in the discrete torsion carried by the S-fold and in the difference in the asymptotic holonomy of the gauge bundle on the 7-brane. These models are connected by an interesting web of RG flows and their Higgs branches provide new examples of instanton moduli spaces.
1st of April 2021, 14:30
Radiation in conformal field theories.
We overview recent developments in the study of radiation in conformal field theories. We show that in conformal field theories including scalar fields, the radiative energy density is not positive definite, the radiated power is not Lorentz invariant and it depends on the derivative of the acceleration. We then discuss the coupling dependence of radiation, and we present unified results for conformal field theories with extended supersymmetry by introducing a novel technique which allows us to calculate the Wilson loop and the partition function for these theories. The results we obtain are all-order expressions in the 't Hooft coupling in the planar limit.
Zoom Meeting ID: 998-7902-4130
1st of December 2020, 14:30
2d (super)gravity and exceptional geometry
Upon torus reduction to two dimensions, (super)gravity theories exhibit an infinite-dimensional group of global symmetries – such as the Geroch group for GR, and E9 for maximal supergravity. These symmetries can be gauged to give rise to more non-trivial dynamics, possibly reflecting flux compactifications on complicated backgrounds. For instance, AdS2 solutions in 2d gauged supergravity may arise from reduction on the compact part of black hole near-horizon geometries. The full structure of these gauged models has so far been elusive and little is known about the flux compactifications leading to them.
I will describe the construction of exceptional field theory for affine Lie algebras, a formalism that promotes the (Geroch/E9) symmetries of 2d (super)gravity to formal invariances of their higher-dimensional parent theories, which greatly simplifies the study of certain classes of flux compactifications and should help us complete the construction of the associated two-dimensional gauged models.
Zoom Meeting ID: 998-7902-4130
17th of November 2020, 14:30
Quantum extremal islands made easy
Recent discussions of the information paradox involve rather puzzling regions in spacetime called ‘Quantum extremal islands’. We show how these are easily understood from the standard Ryu-Takayanagi formula in the presence of Randall-Sundrum branes in arbitrary dimensions.
10th of November 2020, 14:30
Type B anomalies (Mis-)Matching
In this talk we analyse several aspects related to type B conformal anomalies associated with Coulomb branch operators in 4d N=2 SCFTs. In particular, when the vacuum preserves the conformal symmetry, these anomalies coincide with the two point function coefficients in the Coulomb branch chiral ring. We analyse the behaviour of these anomalies on the Higgs branch, where conformal symmetry is spontaneously broken. We review the argument developed in arXiv:1911.05827
and, following it, we argue that these anomalies are covariantly constant on conformal manifolds. In some cases this can be used to show that the anomalies match in the broken and unbroken phases. Then, in the second part of the talk, we focus on some specific 4d N=2 SCFTs and we test type B anomaly (Mis-)Matching through an explicit Feynman diagram computation. We finally observe that an implication of Type B anomaly Mismatching is the existence of a second covariantly constant metric on the conformal manifold that imposes restrictions on its holonomy group.
Zoom Meeting ID: 998-7902-4130
3rd of November 2020, 14:30
Deconfining class S theories
Class S theories are a broad and interesting class of N=2 superconformal field theories arising from wrapping the six dimensional (2,0) theory on Riemann surfaces. Most of these theories have no known Lagrangian description.
I will present a method (based on brane engineering) that allows to systematically construct N=1 Lagrangians flowing to some of these N=2 theories. As an illustration of the method, I will construct a Lagrangian description for the simplest non- trivial class-S theory, the \(T_3\) theory with global symmetry \(E_6\), and for some related examples.
20th of October 2020, 14:30
Bootstrapping defects and boundaries for the free scalar field
Is there any room for non-trivial unitary and conformal defects in the theory of a single free massless scalar field? And what about boundaries? We use the free scalar equation of motion and the structure of the bulk-to-defect operator expansion to rule out the existence of such defects in several (co-)dimensions. For boundaries we are led to a non-trivial system of crossing equations that we analyze numerically in four bulk dimensions. We show that large regions of parameter spaces are excluded, but a ‘kink’ in the numerical bounds obeys all our consistency checks and might be an indication of a new conformal boundary condition.
Zoom Meeting ID: 998-7902-4130
13th of October 2020, 14:30
The fate of discrete 1-form symmetries in 6d
Recently introduced generalized global symmetries have been useful in order to understand non-perturbative aspects of quantum field theories in four and lower dimensions. In this talk I will focus on 1-form symmetries of weakly coupled 6d supersymmetric gauge theories coupled to tensor multiplets and their interplay with large gauge transformations for dynamical tensor fields. In a non-trivial background for the global 1-form symmetry, this leads to an ambiguity of the effective field theory partition function. This anomaly is eliminated by the inclusion of BPS strings. However, the non-trivial 1-form background can induce fractional string charges which are not compatible with Dirac quantization, and hence the symmetry is absent. I will describe how the anomalous term serves as a tool to detect whether the discrete 1-form symmetries are realized in explicit examples originating from string compactifications. I will show how this is corroborated by finding that a non-trivial ambiguity is related to states, which are excitations of the 6d BPS strings and explicitly break the global 1-form symmetry. For 6d theories consistently coupled to gravity, this ambiguity of the partition function hints at the presence of a symmetry breaking tower of states. When the ambiguity is absent, the F-theory realization of the theories points to the gauging of the 1-form symmetries.
6th of October 2020, 14:30
Large charges in QFT
It has been very recently realized that large charge sectors in QFT’s exhibit interesting properties and simplifications. In this talk we will discuss two particular examples, namely the case of N=2 superconformal QCD in d=4 and the case of the Wilson-Fisher fixed point in various dimensions. It turns out that it is possible to find different regimes if the coupling of the theory scales appropriately with the charge, thus finding a variety of interesting behaviors.
29th of September 2020, 15:30
3d S-fold SCFTs
A local SL(2,Z) transformation on the Type IIB brane configuration
gives rise to an interesting class of 3d superconformal field
theories, known as the S-fold SCFTs. One of the interesting features
of such a theory is that, in general, it does not admit a conventional
Lagrangian description. Nevertheless, it can be described by a quiver
diagram with a link being a superconformal field theory, known as the
T(U(N)) theory. In this talk, we discuss various interesting
properties of the S-fold theories, including supersymmetry enhancement
in the infrared as well as several interesting dualities.